Improvement relating to drill rods

ABSTRACT

In one aspect the present invention may be said to comprise a drill rod for assembly with other drill rods to form a drillstring used for fluid reverse circulation drilling comprising: an outer drill rod comprising a bore that is tapered at each end, an inner drill rod within the outer drill rod, and a retention member removably coupled to each end of the inner drill rod to retain the inner drill rod between the tapered ends of the outer drill rod.

FIELD OF THE INVENTION

The present invention relates to fluid RC drilling, core sampling anddual walled drill rods for use in fluid RC drilling that can then beconverted to drill rods for core sampling.

BACKGROUND TO THE INVENTION

In mineral and/or sub terrain exploration, typically one and/or twodrilling processes are used to get to the zone of interest in aformation after the initial borehole has been collared to prevent holecollapse. One of the two processes is reverse circulation (RC) drillingthat allows chip samples to be obtained from the formation which can bebrought back to surface for analysis while drilling the borehole. Thesecond of the two processes is core drilling that allows a core sampleto be obtained of the formation that provides accurate information ofthe formation. Generally, core drilling is undertaken after the zone ofinterest in the formation has been reached using the RC drillingprocess, although in some instances the driller may decide to just usecore drilling. It is appreciated that core drilling is slower by thefact the process must stop in order to retrieve the core sample.

With traditional RC drilling, the total apparatus includes a large heavydrill rig, compressors and a drillstring that is assembled from aplurality of heavy, double walled drill rods, and any other componentsrequired to carry out the RC drilling process, such as hammers, bits andthe like. For core drilling, this is carried out with a significantlysmaller drill rig, there is no requirement for compressors and thedrillstring is assembled from lightweight drill rods and othercomponents such as a wireline retrievable core barrel, coring bits etc.and other components that are lowered into the bore hole. This processoccurs after the RC drillstring has been removed and then operated tocarry out coring.

RC drilling is a process that typically requires significant power inputin order to drive the hammer downhole in the form of low speed/hightorque drives. As such in prior art systems, pneumatic RC drilling isundertaken where large compressors are used to drive the pneumatichammer. The use of such large compressors and therefore pneumatichammers, creates significant pressures, which then requires drill rodsthat can withstand such pressures. Consequently, the drill rods are madeof strong materials, such as steel or the like, that then makes thedrill rods heavy therefore the drillstring becomes heavy, which thenrequires an equally strong and robust drill rig frame, that is alsoheavy to hoist and lower the drillstring whether uphole or downhole.These additional weights consequently require more power to drive theentire system leading to increased power inputs. For example, aconventional 3.5″ RC rod used for conventional air RC drilling systemsweighs approx. 67 Kgs per 3 metre length. So, for a 250 m drillstring,the drill rods alone weigh approximately 5600 kg. As a result, thedrillstring is very heavy and requires a heavy-duty drill rig to operatethe drillstring. The heavy-duty drill rig may be truck or track mountedwith the addition of the necessary compressors to drive the largersystem.

In comparison, core sample drilling requires an accurate analysis of theformation where the core sample must be kept intact. Thus, the use ofcompressors and high-powered hammers etc. used in RC drilling isreplaced with a high speed/low torque drive. As the high pressures arenot present, the drill rods used are light weight, typically approx. 40kg per 3 meter length, consequently the drillstring is lighter (3333 kgfor a 250 m drillstring) and therefore the need for a heavy-duty drillrig as used in RC drilling is not necessary.

SUMMARY OF INVENTION

It is an objection of the invention to provide a drill rod for that canbe converted from a drill rod RC drilling to a drill rod for core sampledrilling and/or associated apparatus formed from the drill rod.

In one aspect the present invention may be said to comprise a drill rodfor assembly with other drill rods to form a drillstring used for fluidreverse circulation drilling comprising: an outer drill rod comprising abore that is tapered at each end, an inner drill rod within the outerdrill rod, and a retention member removably coupled to each end of theinner drill rod to retain the inner drill rod between the tapered endsof the outer drill rod.

In another aspect the present invention may be said to comprise a drillrod for assembly with other drills rods to form a drillstring used forfluid reverse circulation drilling comprising: an outer drill rodcomprising a lightweight drill rod used in core drilling with a borethat is tapered at each end, an inner drill rod within the outer drillrod, and a retention member removably coupled to each end of the innerdrill rod to retain the inner drill rod between the tapered ends of theouter drill rod.

Optionally the retention member comprises a first retention membercoupled to a first end of the inner drill rod, and a second retentionmember coupled to a second end of the inner drill rod.

Optionally the first and/or second retention member comprises: acoupling by which the retention member can be removably coupled to arespective end of the inner drill rod, and a radially extending abutmentconfigurable to abut on a respective taper of the bore, the abutmentcomprising: a fixed portion with a diameter less than the smallestdiameter of the bore, a deployable element to extend the diameter of theabutment greater than the smallest diameter of the bore.

Optionally: the fixed portion of the abutment comprises two or moreradial arms, the deployable element comprises at least one element in ineach radial arm that can deploy from the radial end of the arm.

Optionally the element deploys when the inner drill rod is coupled tothe retention member.

Optionally the outer drill rod is a lightweight drill rod.

Optionally the outer drill rod is a diamond drill rod, coring drill rod,H rod or the like.

Optionally the inner drill rod inner has an outer diameter less than thesmallest diameter of the bore of the outer drill rod.

In another aspect the present invention may be said to comprise aretention member for a drill rod for assembly with other drill rods toform a drillstring used for fluid reverse circulation drillingcomprising: a coupling by which the retention member can be removablycoupled to an end of an inner drill rod, and a radially extendingabutment configurable to abut on a respective taper of a bore of alightweight outer drill rod, the abutment comprising: a fixed portionwith a diameter less than the smallest diameter of the bore, adeployable element to extend the diameter of the abutment greater thanthe smallest diameter of the bore.

Optionally: the fixed portion of the abutment comprises two or moreradial arms, the deployable element comprises at least one element in ineach radial arm that can deploy from the radial end of the arm.

Optionally the element deploys when an inner drill rod is coupled to theretention member.

In another aspect the present invention may be said to comprise a methodof assembling a dual walled drill rod for subsequent assembly with otherdrill rods to form a “drillstring” used for fluid reverse circulationdrilling, the method comprising taking an outer drill rod comprising abore that is tapered at each end and: doing one of: coupling a firstretention member to a first end of an inner drill rod, the firstretention member having a radially extending abutment with a deployableelement, and inserting the first retention member and inner drill rodinto the bore of the outer drill rod, or inserting a first retentionmember into the bore of the outer drill rod, the first retention memberhaving a radially extending abutment with a deployable element, andinserting an inner drill rod into the bore of the outer drill rod andcoupling the inner drill rod to the first retention member, anddeploying the deployable element of the radially extending abutment ofthe first retention member, coupling a second retention member to asecond end of the drill rod, the second retention member having aradially extending abutment with a deployable element, and deploying thedeployable element of the radially extending abutment of the secondretention member.

Optionally the dual walled drill rod is anyone of those in thestatements above.

In another aspect the present invention may be said to comprise a methodof disassembling a dual walled drill rod, being a drill rod of any ofthe statements above so that an outer drill rod of the dual walled drillrod can be assembled with other drill rods to form a drillstring usedfor core sampling, the method comprising: undeploying the deployableelement of the radially extending abutment of the second retentionmember, and removing the second retention member from the bore of theouter drill rod, and one of: undeploying the deployable element of theradially extending abutment of the first retention member, and removingthe inner drill rod and first retention member from the bore of theouter drill rod.

In another aspect the present invention may be said to comprise methodof RC drilling and core sampling comprising: assembling a firstdrillstring with dual walled drill rods according to any statement aboveand/or using the assembly method of any statement above, operating thefirst drillstring using a lightweight drill rig to perform fluid RCdrilling, resulting in a borehole, upon completion of RC drilling,extracting the drill string from the borehole, disassembling the drillrods of the first drillstring according to any statement above,assembling a second drillstring with the outer drill rods, along withcore sampling components, deploying and operating the second drillstringin the borehole using the lightweight drill rig to perform a coresampling.

It is intended that reference to a range of numbers disclosed herein(for example, 1 to 10) also incorporates reference to all rationalnumbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5,7, 8, 9 and 10) and also any range of rational numbers within that range(for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7).

The term “comprising” as used in this specification means “consisting atleast in part of”. Related terms such as “comprise” and “comprised” areto be interpreted in the same manner.

This invention may also be said broadly to consist in the parts,elements and features referred to or indicated in the specification ofthe application, individually or collectively, and any or allcombinations of any two or more of said parts, elements or features, andwhere specific integers are mentioned herein which have knownequivalents in the art to which this invention relates, such knownequivalents are deemed to be incorporated herein as if individually setforth.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments will now be described, with reference to the followingdrawings, of which:

FIG. 1 shows a drill rig and drill string for fluid RC drilling.

FIG. 2 shows a dual walled drill rod in generic form.

FIG. 3 shows a first embodiment of an assembled dual walled drill rod.

FIGS. 4-6 shows a first embodiment of the dual walled drill rod in theuphole, neutral and downhole positions to illustrate the inner rod“float” when the retention members (24A and 24B) of FIGS. 7A and 7B areattached.

FIG. 7A, 7B show first and second embodiments of a retention member forthe dual walled drill rod.

FIG. 8 shows an inner drill rod of the dual walled drill rod.

FIGS. 9 to 13B show stages of an assembly of a dual walled drill rod.

FIG. 14 shows a tool for assembling the dual walled drill rod.

FIGS. 15 to 19 show stages of an alternative assembly of a dual walleddrill rod.

FIG. 20 shows in diagrammatic form one embodiment of a core samplingassembly and of the direction of fluid flow in an assembled dual walleddrill string of the present invention while in use downhole.

FIG. 21 shows in diagrammatic form a core catcher and drill bitarrangement used in the core sampling assembly of FIG. 20 .

FIGS. 22A, 22B shows an example of a core catcher barrel and drillstringassembly.

FIG. 23 shows an example of fluid flow through a core catcher barrel anddrillstring assembly

DETAILED DESCRIPTION OF EMBODIMENTS Overview

The embodiments described provide a dual walled drill rod for assemblywith other such drill rods to form a drillstring to be used for fluidreverse circulation (RC) drilling. These same dual walled drill rods canthen be disassembled to be used again in wireline core sample drilling.So these drill rods are a hybrid drill rod that can be converted from adual wall drill rod for assembly for RC drilling to a lightweight drillrod to be used for wireline core sample drilling.

FIG. 1 shows in diagrammatic form a drill rig 15 and drillstring 10 toprovide fluid reverse circulation (RC) drilling, in order to drill aborehole 11. Chip samples can be obtained during the RC drilling processthat are then used for analysis of the formation. Once the RC drillingprocess is completed, coring can take place to provide a more accurateanalysis of the formation (using the outer drill rods of the rods usedin RC (i.e., removal of the inner) drilling to make up a separatedrillstring for coring as described later).

Due to the lightweight nature of the drill rods, the drillstring 10 isoperated by a lightweight diamond drilling/coring drill rig 15.Hereinafter, the drill rig will be referred to as a “lightweight drillrig”. The drillstring for fluid RC drilling comprises a plurality ofdual walled drill rods (e.g. 12) coupled together, the dual walled drillrods being those as described herein. The drillstring 10 can compriseother components for fluid RC drilling such as a fluid operatedhammering apparatus 13 and a drill bit 14. Drillstrings and thecomponents therein will be known to those skilled in the art.

As will be described later, the dual walled drill rods 12 comprise,among other things, a lightweight drill rod as the outer part of thedrill rod. Any suitable lightweight drill rod could be used, typicallythose called “wireline core sample drill rods”, “diamond drill rods”,“coring drill rods”, drill rods having an “internal upset” or are“double butted” where “butted” means the bore of the drill rod istapered at both ends.

The use of a lightweight drill rod (e.g. wireline core sample drillingrod) for RC drilling is enabled through the use of a fluid thatactivates a fluid activated apparatus such as a fluid activated hammeror vibrational apparatus, and carries the chips to surface (rather thanusing pneumatic RC drilling that uses heavy walled drill rods and heavydrill rigs). The use of such a lightweight outer drill rod provides alightweight drillstring, which in turn can be operated by a lightweightdrill rig. The use of such a lightweight drill rig provides advantagesin the coring field of use. The same type of lightweight outer drillrods can be used for both the fluid RC drilling process and the coringprocess. That means, the same lightweight drill rig and same outerlightweight drill rods can be used for coring and with the addition ofan inner rod of the present invention can then be used for RC drilling.The drill rig does not have to be changed between the fluid RC drillingchip sampling process, and the core sampling process. This significantlyreduces costs and time lost thus leading to greater overallefficiencies.

FIG. 2 shows in general diagrammatic form a dual walled drill rod 12according to the embodiments described that can be assembled with othersuch dual walled drill rods to form a drillstring 10 for fluid RCdrilling. Reference herein to “drill rod” will mean the dual walleddrill rod 12.

Drill rod 12 comprises a (lightweight) outer drill rod 20 (“host rod”)that is typically used in diamond drilling and is lighter weight thanthat used in pneumatic RC drilling as the drill rod for fluid RCdrilling only needs to carry fluid (such as drilling fluid such as mud),rather than contain the significant air pressures present in pneumaticRC drilling.

Generally, when reference is made to a drill rod being lightweight, thismeans a lightweight drill rod e.g. for wireline core sampling that islighter than conventional RC drill rods although still has sufficientstrength to carry on its purpose. The lightweight drill rod can be madelighter through constructing the same from different materials, such asaluminium, lower grade steel, etc or the rod can still be made with thesame materials as for an RC rod, such as steel, but the thickness isless. The weight differences can be as much as a 60% weight reductionalthough typically is around a 40-50% difference. The reason the drillrod can be made lighter is that the lightweight rod need only carry afluid rather than have to withstand the significant air pressuresexperienced with the typically used pneumatic hammer for RC drilling.Examples of types of lightweight outer drill rods that can be used canbe defined by one or more of the following characteristics:

-   -   A wireline coring drill rod designed for use with        non-compressible drilling fluid.    -   For use in diamond core drilling.    -   Weights—e.g. about 40 kg or less (compared with 75 kgs for other        types of RC drill rods).    -   Examples of such lightweight wireline coring rods can be found        in any one of the following technical specification sheets at        -   Boart Longyear™ Coring Rods and Casing Catalog found at:        -   http://app.boartlongyear.com/brochures/2016-Coring_Rods_Casing-Catalog-F9.pdf.        -   Fordia            https://www.fordia.com/wp-content/uploads/2015/11/fichetechniquehuskyangweb.pdf        -   Di-Corp            https://www.di-corp.com/products/view-product/deep-hole-wireline-drill-rodor            Global Geotech            https://www.globalgeotech.co.uk/drill-rods-casing-tubes.htm    -   Note, the above are just examples and are not exhaustive of the        types of lightweight drill rods that could be used with the        present embodiments.

A particular non-limiting example could be as follows:

-   -   H rod.    -   V wall rod with a bore of the rod with an internal taper. The        bore is “internally upset” or “double butted”. “Butt”, means        that the ends of the rod are tapered.    -   Designed for use with non-compressible drilling fluid.    -   For use in diamond core drilling.    -   Weights—e.g. 40 kg (compared with 67 kgs for other types of RC        drill rods).    -   Generally, an H rod is 3.5 inches in diameter and fits/suits the        “chuck drive” on a diamond drill rig. The chuck drive is a        hollow spindle that generally has 5-7 teeth internal of the        spindle that hydraulically grip/grab the rod at the top of the        hole to provide Weight On Bit (WOB) and rotation to the rods in        use. Also, the diamond drill rig, may have a “foot clamp” that        is designed to fit/receive these H rods at the base of the rod.

For example, a “H-wireline coring rod with an internal upset” could beused. “Upset” refers to the internal diameter ends of the rod beingthicker than the majority of the body of the rod.

The taper or upset serves the purpose of thickening the rod at eitherend to enable functional threads (male and female) to be made to allowsuitably strong connections of the rods together.

The outer drill rod 20 is a hollow cylinder/cylindrical wall with a bore21. The bore 21 has a varying diameter, and comprises:

-   -   a (preferably fixed diameter) central section 21A,    -   a varying diameter tapering section 21B, 21C extending from each        end of the central section, each taper section leading to a    -   a (preferably fixed diameter) end section 21D, 21E, leading to a    -   bore opening 20A, 20B at each end of the outer drill rod.

The diameter of the central section 21A is larger/wider than thediameter of the two end sections 21D, 21E/bore openings 20A, 20B (whichare smaller/narrower than the diameter of the central section). Thetapered sections 21B, 21C are shown exaggerated in FIG. 2 for clarity.In practice, that taper is much smaller but sufficient to allow themachining of the threads.

The dual walled drill rod has an inner drill rod 22 which is a hollowcylinder (tube)/cylindrical wall with a bore 23. Each end 22A, 22B ofthe inner drill rod is removably coupled to a retention member 24. Inthe preferred embodiment, there are two retention members 24A, 24B thatdiffer slightly to have reciprocal couplings. Reference to retentionmember 24 can mean either of these variations. The retention member 24comprises a radially extending stop/abutment 25 (25A, 25B), a firstcoupling configured for coupling to one end of the inner drill rod 22,and a second coupling configured for coupling to an end of acorresponding retention member of an adjacent dual walled drill rod(e.g. 12 A—see FIG. 1 ) to which the dual walled drill rod will becoupled. The radially extending abutments 25A, 25B comprise fixedportions 26A, 26B (collectively referred to as 26) having a diameterless than the narrowest/smallest diameter of the outer drill rod bore(being the diameter of the opening 20A, 20B/end section 21D, 21E) of thebore) and it has deployable portions (element) 27A, 27B (collectivelyreferred to as 27) that extends from the diameter of the abutment 25A,25B to be greater than the smallest diameter of the outer drill rodbore. The deployable portion 27 could be any suitable element such as aball, but other options are possible also, such as rods, springs, camrollers, lobes or the like.

When a retention member 24 is coupled to each end of the inner drill rod22, and the deployable portion 27 is deployed, the diameter of theradially extending abutment 25 will be greater than that of thenarrowest diameter 21D, 21E of the bore 21 of the outer drill rod. Thismeans that the inner drill rod 22 will be retained within the outerdrill rod 20 and between the narrow openings/end sections as theradially extending abutment will prevent the inner drill rod extendingpast the tapered sections 21B, 21C at either end of the outer drill rodbore 21. When abutment 25 abuts the tapered section, it could be deemedto be seated, and the abutment could also be considered a “seat”. Theterm “seat” and “abutment” can be used interchangeably in thisspecification in relation to this component of any of the embodiments ofthe retention member. The radially extending abutment 25 will notnecessarily touch or engage with the tapered sections, although it cando so. This allows the inner drill rod to have a freedom of movement(tolerance) to “float” between the two end sections 21D, 21E within thebore 21 to prevent the inner rod damaging the two end sections when thedual walled drill rod is vertical and assembled into a drillstring. The“float” or range of movement is dictated in part by the upholeconnections, such as the drill rig 15 and downhole connections, such asthe hammer 13 and bit 14. Having this float/tolerance allows the innerrods a range of movement to accommodate these uphole and downholeconnections, that also takes into account any manufacturing tolerancesof the outer drill rods when placed into the vertical position. Thisthen allows the abutments to seat into the tapered sections withoutdamaging them. It should be noted that the inner rod is non-rotationallylinked to the outer—so when the outer rods are being tightened up ortwisted together, it does not interfere with the inner rods.

The dual walled drill rod 12 is assembled generally as follows. First,an outer drill rod 20 is taken. Then, a first retention member 24A, asecond retention member 24B and the inner drill rod 22 are assembled ina suitable sequence and inserted into the outer drill rod bore 21 in asuitable sequence. The deployable portion 27A, 27B is deployed to retainthe inner drill rod 22 within the outer drill rod 20. In one possibleembodiment, deployment is achieved by partially coupling the inner drillrod 22 to the first retention member 24A and placing the assembly intothe outer drill rod 20, then deploying the deployable portion 27A sothat the retention member 24A seats within the tapered section 21B andtherefore inner drill rod 22 cannot go past the end section 21D of theouter drill rod 20. The second retention member 24B is placed into theouter drill rod bore 20 and coupled to the inner drill rod 22, and thedeployable portion 27B is deployed, so that the inner drill rod 22 andsecond retaining member 24B seats within the tapered section 21C andtherefore cannot go past the end section 21E of the outer drill rod 20.It will be appreciated that there are many other arrangements, andsequences and methodologies for assembling the inner drill rod withinthe outer drill rod. Some will be described in further detail later.

A plurality of such a dual walled drill rods 12 can be assembled, andthen they can each be assembled with an adjacent dual walled drill e.g.12A rod to create a drillstring 10.

Example Embodiments

A detailed description of one possible example embodiment of thelightweight dual walled drill rod will now be described with referenceto FIGS. 3 to 8 .

FIG. 3 shows an assembly of the dual walled drill rod 12, itself coupledto two adjacent identical dual walled drill rods 12A, together formingpart of a drillstring 10.

The drill rod 12 comprises an outer drill rod 20 which is a hollowcylinder/cylindrical wall with a bore 21. The bore comprises a centralsection 21A of fixed diameter extending to a narrowing tapered section21B, 21C of reducing diameter at each end of the central section 21A,and each tapered section extending to an end section 21D, 21E with anopening 20A, 20B (see FIG. 2 ). The end section and opening are of afixed diameter that is smaller/narrower than the central section 21Adiameter. Each end 20A, 20B of the outer drill rod 20 comprises aninternal thread 31A, 31B or other coupling section for coupling to anadjacent drill rod 12A.

The drill rod further comprises an inner drill rod 22 formed of a hollowcylinder with a bore 23 of fixed diameter (seen in more detail in FIG. 8). Each end 22A, 22B of the inner drill rod comprises an outer/externalthread 32A, 32B or other coupling for coupling the respective end of theinner drill rod to a respective retention member (e.g. spigot) 24A, 24B.

There are two types of retention members 24A, 24B, each for coupling toan opposite end 22A, 22B of the inner drill rod. The retention members24A, 24B can be seen in more detail in FIGS. 7A, 7B. A first retentionmember (variation/embodiment—see FIG. 7A) comprises a hollowcylinder/cylindrical body 71A with a bore 72A that forms an extensionsection. A radially extending abutment 25A protrudes radial from one endof the cylindrical body 71A. The abutment has a hollow central portion74A that provides an opening to the bore 72A of the cylindrical body.The retention member comprises a first coupling 73A (for example at afirst end) in the form of an internal thread or other suitable couplingfor connection to the external thread 32A or other coupling of the innerdrill rod. The first coupling 73A is preferably provided within the bore72A of the cylindrical body, although this is not essential. Theretention member comprises a second coupling 75A (for example at asecond end) in the form of a bayonet or other suitable coupling forcoupling to a corresponding second retention member 25B on an adjacentdrill rod 12A. The second coupling is preferably provided at the end ofthe cylindrical body away from the radially extending abutment, but thisis not essential. Further provided about the second coupling is a seal33A to be received within a cavity 34A or the like that retains theseal. The seal 33A can be more clearly seen in FIG. 9 .

The radially extending abutment 25A comprises a plurality (preferablyfour) of lugs e.g. 76A that extend radially from the cylindrical bodyand are spaced such that there are gaps 77A between adjacent lugs. Thegaps allow fluid flow either up or downhole, preferably downhole. Eachlug 76A has a spherical cavity 78A for receiving a deployable ball 27A.Each cavity 78A comprises ball opening 79A on the internal surface ofthe central opening 74A of the abutment with a diameter greater than thediameter of the ball to allow insertion of the ball, and retentionopening 70A on the outer surface of the lug 76A with a diameter that isless than the diameter of the ball so that the ball can protrude throughthe opening, but cannot pass through the opening so the ball is retainedin the cavity. Further retention of the ball can be aided by theprovision of an O-ring 80A (see FIG. 9 ) or the like within thespherical cavity 78A to prevent the ball falling out. In a manner to bedescribed more fully later, upon full insertion and coupling of theinner drill rod 22 to the retention member 25A, the deployable ball ineach lug will deploy by partially extending through the retentionopening on the outer surface of the lug.

A second retention member 25B (variation/embodiment—see FIG. 7B) isprovided, which is configured in the same as the first retaining member25A, except that the second coupling 75B (for example at a second end)is in the form of a socket for receiving the bayonet coupling 75A of thefirst retention member. On the bayonet coupling being received withinthe socket, the seal 33A sealingly engages to the internal diameter ofthe socket 72B to prevent fluid escaping. The reference numerals in FIG.7B suffixed with “B” correspond to the same reference numerals in FIG.7A suffixed with “A” for the same feature (e.g. 71A, 71B), or a featurewhich is not the same, but is similar or corresponding (e.g. 72A, 72B).More generally, a reference with no suffix can be used as shorthand torefer to either retention member embodiment.

When fully assembled, the retention members 24 and inner drill rod 22sit within the bore 21 of the outer drill rod 20. In particular, theassembly sits movably within the central 21A and tapered sections 21B,21C of the bore 21. The deployable balls 27A, 27B are deployed such thatthey protrude through the cavity retention openings in the lugs andprovide a deployed diameter of the retaining member abutment that islarger than the diameter of the end sections/openings of the outer drillrod bore. This means that the inner drill rod cannot move past thetapered sections 21B, 21C of the outer drill rod bore 21 and thereforeis retained there within. As the first and second embodiments 24A, 24Bof retention members work together in this fashion, together they canjointly be considered a “retention member”. The cylindrical body 71(comprising 71A, 71B) of each retention member 24 has a diameter that isnarrower than the diameter of the end section/opening of the outer drillrod bore, and therefore the cylindrical body 71 can extend therethrough.The cylindrical body 71A of the first retention member 24A isdimensioned so that it in fact extends through and beyond the opening ofthe outer drill rod bore so that it can extend into the opening of thebore of an adjacent drill rod and its bayonet 75A can couple to thesocket 75B of the cylindrical body 71B of the second retention member24A of the adjacent drill rod 12A. Likewise, the cylindrical body 71B ofthe second retention member 24B is dimensioned so that it extends intothe opening of the outer drill rod bore 21 and the socket coupling 75Bcan receive the bayonet coupling 75A of the corresponding retentionmember 24A of a corresponding adjacent drill rod 12A.

FIGS. 4 to 6 show how the inner drill rod 22 and retention memberassembly 24 is retained within the outer drill rod bore 21, yet can movelongitudinally within the central 21A and tapered sections 21B, 21C.During operation, the drillstring 10 is vertical and dependent on theuphole and downhole connections the inner drill rod 22 and respectiveretention member assemblies 24A, 24B can move uphole or down hole due tothe “float” (that is, tolerance/built in allowed range of movement) tosome degree within the bore 21 of the outer drill rod 20. FIG. 4 showsthe inner drill rods/retention member assembly floating towards uphole(left hand side of the figure), such that the uphole abutment 24A iswithin the tapered section 21B and the downhole abutment 24B is withinthe central section 21. FIG. 5 shows the assembly floating in a neutralposition, such that both the uphole abutment 24A and downhole abutment24B sit on the boundary of the respective tapered sections 21B, 21C andcentral section 21A. FIG. 6 shows the inner drill rods/retention memberassembly floating towards downhole (right hand side of the Figure), suchthat the uphole abutment 24A is within the central section 21 and thedownhole abutment 24B is within the downhole tapered section 21C. Thismovement into, at and out of the respective tapered sections dependsupon the uphole (drill rig 15) and downhole connections (hammer 13 andbit 14).

Method of Assembly and Disassembly of the Dual Walled Drill Rod

A method of installing the retention members to an inner drill rod thatis also installed into the outer drill rod to assemble the dual walleddrill rod will now be described in detail. It will be appreciated thatthe order and sequence is one example only, and others will be envisagedby those skilled in the art.

Referring to FIG. 9 , a first end of an inner drill rod 22 is threadedlycoupled to the threaded first coupling 73A inside the retention member24A. However, at this point the inner drill rod 22 is only partiallythreaded on, so that some of the external thread 32A (see FIG. 8 ) onthe inner drill rod is still exposed within the retention member centralopening 74A. This means that the full diameter/width of the inner drillrod is not positioned concentrically between the deployable balls, so asnot to deploy them. Rather, the slightly narrower threaded portion 32Ais concentrically between the spherical balls, so does not deploy theballs such that the balls are still flush inside the retention member.This means the radially extending abutment has a diameter that is lessthan the diameter of the end section/bore opening to the outer drill rodso that the retention member and inner drill rod can slide into theouter drill rod bore. In this case the first embodiment of the retentionmember 24A with a bayonet (second) coupling 75A is shown, but theprocess could equally apply to the second embodiment of the retentionmember 24B with the socket (second) coupling 75B.

Referring to FIG. 10 , next, the retention member 24A/inner drill rod 22assembly is inserted (with the retention member leading) into an outerdrill rod 20 in direction A. A castellated tool 140 (such as shown inFIG. 14 ) or other suitable tool is used to rotate, tighten and fullycouple the inner drill rod and the retention member. Referring to FIG.14 , the castellated tool has a hollow cylindrical body with cut-outsand turrets at one end to form the castellation. At the opposite end thebody is provided with a pair of complementary flat sides 141 and a slotinto which an actuation handle 142 is provided. The tool is insertedinto the bore 21 of the outer drill rod 20 into the gap between theinner drill rod 22 and the outer drill rod 20 and the castellations ofthe tool align and engage in the lugs/gaps between the lugs of theretention member. The castellated tool can then be held still by the useof a spanner or the like that grips the flat sides of the tool, theinner drill rod can then be rotated to fully engage the remaining threadof the inner rod bringing the two together into a full couplingposition. In this position, the full outer width/diameter of the innerdrill rod 22 moves into position concentrically within the abutmentopening 74A and between the balls. This movement deploys the deployableballs, so they protrude through the retention openings in the lug. Thiscan be seen in FIG. 10 where the balls are now deployed within the borewall 21A and inside the tapered section 21C.The abutment 25A is now inthe fully deployed configuration such that its diameter is now largerthan the diameter of the end section 21B, 21C/openings 20A, 20B of theouter drill rod bore 21.

Referring to FIG. 11 , the inner drill rod is then pushed further, againin direction A, into the bore of the outer drill rod until the thread orother coupling on the other end of the inner drill rod is just exposed.Referring to FIG. 12 , next a retention member according to the secondembodiment 24B is coupled to the exposed thread 32B of the inner drillrod 22. Again, at this point the inner drill rod 22 is only partiallythreaded on, so that some of the external thread on the rod is stillexposed within the retention member 24B. This means that the full widthof the inner drill rod 22 is not positioned concentrically between thedeployable balls, so as not to deploy them. Rather, the slightlynarrower threaded portion is concentric with the balls, so does notdeploy them. This means the radially extending abutment has awidth/diameter that is less than the diameter of the end sections21B,21C/opening 20A, 20B of the outer drill rod 20. In this case thesecond embodiment of the retention member 24B with a socket coupling 73Bis shown, but the process could equally apply to the first embodiment ofthe retention member. In the preferred embodiment, a first embodiment ofthe retention member is coupled to one end, and a second embodiment ofthe retention member is coupled to the opposite end.

Referring to FIGS. 13A and 13B show the opposite ends of an assembledlightweight dual walled drill rod of the present invention where FIG.13A shows retention member 24A with the bayonet coupling and FIG. 13Bshows retention member 24B with the socket coupling. In order to ensurethe retention members are seated correctly between the tapered sections,the inner rod 22/retention member 24A/24B assembly is then pushedfurther into the outer drill rod bore 21 until the first embodimentretention member 24A resides in the tapered portion 21B of the bore. Thefirst retention member cannot push past the tapered portion because thedeployed balls provide an abutment with a width/diameter that will notpass through the smaller diameter of the uphole end section 21B/opening20A of the bore. However, the second embodiment of the retention member24B coupled to the other end of the inner drill rod 22 has not yet beendeployed and will pass through the end section 21C/opening 20B at theother downhole end of the outer drill rod 20 and will not sit within thetapered section 21C of the outer drill rod bore 21 until the inner drillrod is fully threaded into the retention member 24B.

With reference to FIG. 13B and 14 , the castellated tool 140 is thenslid over the cylindrical body 71B of the second embodiment of theretention member 24B and castellations of the tool align and engage inthe lugs/gaps between the lugs of the retention member. To ensure thatthe retention members are located correctly within the inner drill rodthe edges 143 of the handle 142 of the tool sits flush against the end50 of the outer drill rod. A second castellated tool is then slid overthe cylindrical body of retention member 24A. Correct location isnecessary to ensure the balls are deployed in the right position andthat no damage is caused to the tapered sections of the outer drill rod.The first castellated tool can then be rotated with the handle to rotatethe retention member relative to the inner drill rod to thread the twotogether into a full coupling position. In this position, the full outerwidth/diameter of the inner drill rod moves into position concentricallyin the abutment opening between the balls thus pushing the deployableballs, so they deploy and protrude through the openings in the lug. Theabutment is now in the fully deployed configuration such that itsdiameter is now larger than the diameter of the end section 21C/opening20B of the downhole end of the outer drill rod bore 21. Referring toFIGS. 13A,13B, the inner drill rod/retention member assembly is nowretained within the tapered sections of the outer drill rod bore, andthe dual walled drill rod is ready for coupling to other such drill rodsto form a drillstring. The rods can be disassembled in the reversemanner as described further below.

As noted earlier, there are a range of different sequences that theassembly could occur in. For example, an alternative is describedbriefly here with respect to FIGS. 15 to 19 . Referring to FIG. 15 , thefirst embodiment of the retention member 24A is slid into the outerdrill rod bore 21, and then referring to FIG. 16 , the inner drill rod22 is inserted into the drill rod bore and coupled to the secondembodiment of the retention member. The inner drill rod is fully coupledso that the deployable balls of the abutment deploy into their extendedposition (which can be better seen in FIG. 18 ). In a similar manner,the second embodiment of the retention member is coupled to the otherend.

Once the drill rods 12 are made up into a drillstring 10 they are placedon the lightweight drill rig 15 for fluid RC drilling. Referring toFIGS. 4-6 , when a drillstring 10 containing the rod 12, 12A etc islifted from horizontal to vertical, the balls engage in the tapereddownhole section 21C of the drill rods to stop them from dropping out.Preferably, the balls 27A, 27B interlock against the taper—and supportthe weight of the inner drill rod 22. The downhole connection such asthe hammer and/or bit may cause the inner rod to move back uphole tothus engage with the tapered section 21B. The float allows for thismovement to occur and has no effect on mud flows. There could bemultiple ball packs spaced evenly around the abutment in the lugs of theinner rod (four are shown, but other numbers are possible) to keep thelower end of the inner rod concentric to the outer rod. Referring toFIG. 20 , there is shown in schematic a drillstring made up of multiplerods where drilling mud is pumped from surface down the annulus betweenthe inner and outer rod to energise a hammer. The fluid can thenjettison out above the bit into the space between the outer drill rodand the bore hole, where it can then travel down to the bore face wherethe fluid then picks up the cuttings which is then returned to surfacevia the drill bit—through the hammer and up through the centre tube tosurface for analyses. It can equally be envisaged that the fluid comingdown hole could jettison out through the face of the bit and returnuphole between the cavity of the hole and outer drill string.

Preferably, the balls do not touch the tapered sections 21B, 21C untilmoved up or down hole from centre. Their purpose is to stop the innerdrill rod falling out once the rod assembly is lifted into position tobe fitted into the drill string. They do not locate the inner rodaxially. Location of the inner rod is determined by the up and down holeconnections, for example a fluid hammer such as for example a magnetichammer as further described below.

Yet other variations of the assembly are possible. For example, thefirst and second embodiment of retention members could be attached tothe inner drill rod and the entire assembly put into the bore of theouter drill rod, then the first and second embodiment of the retentionmembers are deployed to retain the assembly in place.

Once the fluid RC drilling is complete, the drillstring 10 is removedfrom the bore hole 11 and can then be disassembled into the individualdual walled drill rods. The individual dual walled drill rods aredisassembled, in a manner that is reverse to the process of assembly.

Briefly, the second embodiment of the retention member is partiallyunthreaded from the inner drill rod using the castellated tool so thatthe inner drill rod retracts from the concentric position between thedeployable balls, so that the balls can retract back into the undeployedposition. This can be termed “undeploying” the balls. While the balls donot necessarily retract back at that point (they can retract back laterwhen coerced by the taper) they are in a position where they can retractback. The assembly is then partially pulled out of the outer drill rod.Because the balls can retract back, the second embodiment of theretention member can slide through the smallest diameter bore portion ofthe outer drill rod and be extracted therefrom. The second embodiment ofthe retention member is then fully decoupled from the inner drill rodusing the castellated tool. Next, the inner drill rod is partiallyunthreaded from the first embodiment of the retention member using thetool so that the inner tube retracts from the concentric positionbetween the deployable balls so that the balls can retract back into theundeployed position. This can be termed “undeploying”. The assembly isthen pulled out of the outer drill rod. Because the balls can retractback, the first embodiment of the retention member can slide through thesmallest diameter bore portion of the outer drill rod and be extractedtherefrom. The first embodiment of the retention member is then fullydecoupled from the inner drill rod using the castellated tool. The outerdrill rod can then be repurposed for use in a drillstring for coresampling by coupling to other such drill rods to form a core samplingdrillstring.

As noted earlier, there are a range of different sequences that theassembly and disassembly could occur in.

Once the drill rods 12 have been disassembled, the outer drill rods 20are repurposed (converted) for core sampling, by assembling them into acore sampling drillstring assembly 200. A core sampling drillstringassembly is shown diagrammatically in FIG. 20 . It comprises therepurposed outer drill rods 20 arranged into a drillstring with a bore21. A hammer 13 and coring drill bit 14 and inner core barrel assembly210 are assembled as part of the core sampling drillstring. The innercore barrel assembly 210 and drill bit 14 are shown in more detail inFIG. 21 diagrammatic form. Fluid flow is shown by arrows in both FIGS.20 and 21 .

An example of a core sampling sub-assembly that is attached to the outerrods 20 at the end of the drill string is shown in more detail withreference to FIGS. 22A, 22B and 23 . This apparatus is described in theapplicant's application WO201519193799 (and incorporated herein in itsentirety by way of reference). Referring to FIGS. 22A, 22B and 23 ,briefly, the core sampling sub-assembly comprises an outer casing formedfrom a plurality of outer drill rods 20 coupled together (e.g. throughthreading). The outer casing is or forms part of a drill string. FIG.22B shows the end portion of the apparatus in FIG. 22A that is cut offin FIG. 22A. The outer drill rods 20 forming the drill string 200 isrotated by an up hole drilling apparatus 15. A mechanical forcegenerator (hammer) 13 with an outer tubular housing is coupled to theouter drill rods 20. The outer tubular housing is coupled to the outerdrill rods 20 by threading or other coupling means. A section swivel 211isolates the rotation of the rotational apparatus/mechanical forcegenerator 13 from the core barrel 210. This allows the inner core barrelassembly 210 to rotate relative/independently to the mechanical forcegenerator 13 and to isolate the core sample 212 in the barrel 210 fromrotation that may damage the core sample. To extract a core sample 212,that has been obtained via core sample drilling, the apparatus isadapted to receive an extraction line and assembly that is loweredthrough the centre of the assembled outer drill rods 20 using a cablewire 214 and couples to the extraction sub-assembly 213. The apparatus,including the drilling and hammering operations, are effected by fluidflow from the drilling fluid. FIG. 23 shows the drilling fluid flowpath, by way of example. The hydraulic power is converted into arotational mechanical output by the rotational apparatus (e.g. by aturbine, PDM or the like) and then flows over/through/around themechanical force generator 13 and through the drill bit.

Once the drill rods 12 are made up into a core sampling drillstring, thedrillstring is coupled to the same lightweight drill rig (as for thefluid RC drilling) 15 and the drill rod is deployed into the bore holeand operated by the drill rig for core sampling in the usual way.

Advantages of Embodiments Described

One or more of the following advantages can be experienced from one ormore of the embodiments described.

With prior art pneumatic RC drilling high pressure air is pumped fromsurface down the drill rod—the air energises a pneumatic hammer whichcrushes the rock—and the rock chips are blown to the surface up throughan annulus in the drill bit and pneumatic hammer and up through thecentre annulus of the drill rods—for analyses by a geologist. Aspreviously described, the drill rods used in this application need to bemade of a heavy wall steel tube—(as they are in effect energy storagedevices) as compressed air expands dangerously and if a rod fails thiscan be extremely dangerous. The weight of the RC drill rods dictate thatlarge powerful drill rigs are used, along with very large powerful aircompressors. The deeper the hole—the more weight of rods that are downhole =the bigger the rig needs to be, to be able to pull the rods backout of the hole. Further, the air pressure required increases with thedepth of the hole—thus the deeper the hole, the greater the air pressurerequired, therefore bigger compressors are needed and the requirementfor ever increasing heavy weight drill rods and larger drill rig etc.

In contrast, the present embodiments relate to fluid RC drilling, whichhas been made possible with the applicant's fluid driven hammer andfluid driven vibration technologies (the applicant's technologiesincludes both a Mechanical Force Generator or Magnetic Force Generator(e.g. magnetic hammer is or similar see for example WO2009/028964,WO2012/002827 or Mechanical Force Generator or similar see for exampleWO2012/120403, WO2015/193799 or Magnetic Force Generator or similar seefor example WO2012/161595) that all use a non-compressible drillingfluid (instead of air) to energise the down hole reverse circulation andhammer/vibration apparatus, with the cutting samples being carried tosurface from the drill bit—through the centre of the hammer/vibrationapparatus to surface via the drilling fluid through the dual walleddrill rods for analyses. Fluid does not get pressurised in the same wayair does in this process. Given the fluid driven systems as described,the drill rods for fluid RC drilling no longer need large heavy walleddrill rods due to the non-compressible drilling medium being used. As aresult, fluid RC drilling that utilises such fluid driven hammers orfluid driven vibration apparatus no longer require large drill rigs withexpensive and dangerous air compressors. The present applicants havedetermined that this opens up the potential for lightweight drill rigsand drill strings (e.g. like those for diamond drill rigs for coresampling) to drill deep holes fast (fluid RC drilling) while recoveringa non-contaminated chip sample for mineral analyses, with significantoperational advantages such as for example,

-   -   Easier and cheaper to mobilise drill rigs    -   Safer to use (no compressors/dust)    -   Far less fuel burn (no compressors and smaller rigs)    -   A fluid driven hammer or fluid driven vibration apparatus is not        depth limited (pneumatic RC systems require ever increasing        volumes of compressed air as they get deeper, as well as        struggling when ground water is encountered, it is uncommon for        an air RC system to drill deeper than 500 meters).

A preferred drill bit to be used in the present invention is theapplicant's own hybrid drill bit embodied in WO2018/116140, which isincorporated herein in its entirety by way of reference

Fluid driven hammers and fluid driven vibration apparatus are a recenttechnology from the present applicants (primarily due to the massivechallenges of enabling a hammer or vibration apparatus to operate withmodified drilling fluids (drilling mud)). To date there is nolightweight dual walled reverse circulation drill rods available. Thepresent applicants have determined how to adapt existing lightweightwireline core sampling drill rods to be suitable for use as dual walledlightweight drill rods for reverse circulation.

As an example, “diamond” drill rigs that use lightweight drill stringswith diamond bits for core sampling are the mainstay of mineralexploration, whereby a high-quality rock core sample can be obtained formineral analyses. The embodiments described herein use such lightweightdrill rods which then enables the use of lighter drill rigs than thoseused in pneumatic RC hammers. By way of example—a conventional 3.5″ airRC drill rod weighs approx. 67 kgs. The same size diamond drill rod,will weigh 40 kgs, so a drill will be able to drill approx. 85% deeper(than they would by using air RC Rods), providing significantoperational, safety and cost savings.

In particular, the present applicants have devised how to utilise singlewalled lightweight (e.g. “diamond”) drill rods/wireline core samplingdrill rods, in conjunction with a securely held (but easily removable)inner rod with a threadably energised mechanism that enables the thinwalled diamond drill rod to be quickly and safely modified into a dualwalled light weight RC drill rod (for use with a fluid hammer or fluiddriven vibration apparatus)

The benefit of this approach is that, a lightweight (e.g. “diamond”)drill rig (that being a drill rig capable of rotating thin walled rodsto enable the capture of a rock core sample) is now able to drill deepinto the earths (rock) formations with the fluid driven hammer or fluiddriven vibration apparatus, while capturing samples rock cuttings inreal time for analyses.

Furthermore, once a mineral zone of interest is located, then the fluiddriven apparatus and dual walled RC rods would be withdrawn from theground, the inner rod can then be easily removed, a core sampling barrelattached to the end of the (now) single walled rods, and the coringassembly (using wireline retrievable and/or other systems as arecommonly used) can now be lowered down the existing bore hole andoperated using the existing lightweight drill rig until they reach thedepth where the fluid RC drilling was terminated, and as the coredrilling advances—intact core sample can now be retrieved for analyses.

Normally this process would require two different drill rigs—one large,heavy and expensive to carry out the air RC drilling, and then a secondlighter (diamond drill rig) would be mobilized to take the core samples.Each drill rig would have its own drill rods specific to the functionbeing done.

1. A drill rod for assembly with other drill rods to form a drillstringused for fluid reverse circulation drilling comprising: an outer drillrod comprising a bore that is tapered at each end, an inner drill rodwithin the outer drill rod, and a retention member removably coupled toeach end of the inner drill rod to retain the inner drill rod betweenthe tapered ends of the outer drill rod.
 2. (canceled)
 3. A drill rodaccording to claim 1 wherein the retention member comprises a firstretention member coupled to a first end of the inner drill rod, and asecond retention member coupled to a second end of the inner drill rod.4. A drill rod according to claim 1 wherein the first and/or secondretention member comprises: a coupling by which the retention member canbe removably coupled to a respective end of the inner drill rod, and aradially extending abutment configurable to abut on a respective taperof the bore, the abutment comprising: a fixed portion with a diameterless than the smallest diameter of the bore, a deployable element toextend the diameter of the abutment greater than the smallest diameterof the bore.
 5. A drill rod according to claim 4 wherein: the fixedportion of the abutment comprises two or more radial arms, thedeployable element comprises at least one element in in each radial armthat can deploy from the radial end of the arm.
 6. A drill rod accordingto claim 5 wherein the element deploys when the inner drill rod iscoupled to the retention member.
 7. A drill rod according to claim 1wherein the outer drill rod is a lightweight drill rod.
 8. A drill rodaccording to claim 1 wherein the outer drill rod is a diamond drill rod,wireline coring drill rod, H rod or the like.
 9. A drill rod accordingto claim 1 wherein the inner drill rod inner has an outer diameter lessthan the smallest diameter of the bore of the outer drill rod.
 10. Aretention member for a drill rod for assembly with other drill rods toform a drillstring used for fluid reverse circulation drillingcomprising: a coupling by which the retention member can be removablycoupled to an end of an inner drill rod, and a radially extendingabutment configurable to abut on a respective taper of a bore of alightweight outer drill rod, the abutment comprising: a fixed portionwith a diameter less than the smallest diameter of the bore, adeployable element to extend the diameter of the abutment greater thanthe smallest diameter of the bore.
 11. A retention member according toclaim 10 wherein: the fixed portion of the abutment comprises two ormore radial arms, the deployable element comprises at least one elementin in each radial arm that can deploy from the radial end of the arm.12. A drill rod according to claim 11 wherein the element deploys whenan inner drill rod is coupled to the retention member.
 13. A method ofassembling a dual walled drill rod for subsequent assembly with otherdrill rods to form a “drillstring” used for fluid reverse circulationdrilling, the method comprising taking an outer drill rod comprising abore that is tapered at each end and: doing one of: coupling a firstretention member to a first end of an inner drill rod, the firstretention member having a radially extending abutment with a deployableelement, and inserting the first retention member and inner drill rodinto the bore of the outer drill rod, or inserting a first retentionmember into the bore of the outer drill rod, the first retention memberhaving a radially extending abutment with a deployable element, andinserting an inner drill rod into the bore of the outer drill rod andcoupling the inner drill rod to the first retention member, anddeploying the deployable element of the radially extending abutment ofthe first retention member, coupling a second retention member to asecond end of the drill rod, the second retention member having aradially extending abutment with a deployable element, and deploying thedeployable element of the radially extending abutment of the secondretention member.
 14. A method according claim 13 wherein the dualwalled drill rod comprises the outer drill rod, the inner drill rodwithin the outer drill rod, and the first retention member coupled tothe first end of the inner drill rod to retain the inner drill rodwithin the outer drill rod.
 15. (canceled)
 16. A method of reversecirculation (RC) drilling and core sampling comprising: assembling afirst drillstring with dual walled drill rods according to claim 1,operating the first drillstring using a lightweight drill rig to performfluid RC drilling, resulting in a borehole, upon completion of RCdrilling, extracting the drill string from the borehole, disassemblingthe drill rods of the first drillstring, assembling a second drillstring with the outer drill rods, along with core sampling components,deploying and operating the second drillstring in the borehole using thelightweight drill rig to perform a core sampling.